IBM RackSwitch G8000, Application Manual

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RackSwitch G8000: Application Guide
Figure 26. OSPF Area Types
Types of OSPF Routing Devices
As shown in Figure 27 , OSPF uses the following types of routing devices:
• Internal Router (IR)—a router that has all of its interfaces within the same area.
IRs maintain LSDBs identical to those of other routing devices within the local
area.
• Area Border Router (ABR)—a router that has interfaces in multiple areas. ABRs
maintain one LSDB for each connected area and disseminate routing information
between areas.
• Autonomous System Boundary Router (ASBR)—a router that acts as a gateway
between the OSPF domain and non-OSPF domains, such as RIP, BGP, and
static routes.
Figure 27. OSPF Domain and an Autonomous System
Backbone
Area 0
Stub Area
Not-So-Stubby Area
(NSSA)
Transit Area
No External Routes
from Backbone
Stub Area, NSSA,
or Transit Area
Connected to Backbone
via Virtual Link
(Also a Transit Area)
External LSA
Routes
Internal LSA
Routes
ABR ABR
ABR
ASBR
Non-OSPF Area
RIP/BGP AS
Virtual
Link
ABR
ABR = Area Border Router
ASBR = Autonomous System
Boundary Router
Backbone
Area 0
Area 3
Area 2
Area 1
Inter-Area Routes
(Summary Routes)
ABR
ABR
ABR
ASBR
Internal
Router
ASBR
External
Routes
BGP
RIP
OSPF Autonomous System